The present invention relates generally to the control of exhaust and intake valves during positive power and engine braking. In particular, the present invention is directed to a control valve that combines a check valve and a shuttle valve for use in a lost motion engine brake system. The present invention is also directed to a system and method to allow the clipping or resetting of a lost motion engine brake system.
For many internal combustion engine applications, such as for powering heavy trucks, it is desirable to operate the engine in a braking mode. This approach involves converting the engine into a compressor by cutting off the fuel flow and opening the exhaust valve for each cylinder near the end of the compression stroke.
An early technique for accomplishing the braking effect is disclosed in U.S. Pat. No. 3,220,392 to Cummins, wherein a slave hydraulic piston located over an exhaust valve opens the exhaust valve near the end of the compression stroke of an engine piston with which the exhaust valve is associated. To place the engine into braking mode, the three-way solenoids are energized, which causes pressurized lubricating oil to flow through a control valve, creating a hydraulic link between a master piston and a slave piston. The master piston is displaced inward by an engine element (such as a fuel injector actuating mechanism) periodically in timed relationship with the compression stroke of the engine which in turn actuates a slave piston through hydraulic force to open the exhaust valves. The compression brake system as originally disclosed in the ""392 patent has evolved in many aspects, including improvements on the control valves (see, for example, U.S. Pat. No. 5,386,809 to Reedy et al.; see also U.S. Pat. No. 4,996,957 to Meistrick, which is assigned to the assignee of the present application and incorporated herein by reference.) Improvements have also been made in the piston actuation assembly (see U.S. Pat. No. 4,475,500 to Bostelman). In a typical modem compression braking system, the exhaust valves are normally operated during the engine""s power mode by an exhaust rocker lever. To operate the engine in a braking mode, a control valve separates the braking system into a high pressure circuit and a low pressure circuit using a check valve which prevents flow of high pressure fluid back into the low pressure supply circuit, thereby allowing the formation of a hydraulic link in the high pressure circuit.
Various problems are known in conventional compression braking system. First, a time delay may occur between the actuation of the three-way solenoid valve and the onset of the braking mode. This time delay is due in part to the positioning of the solenoid valve a spaced distance from the control valve, which creates longer than ideal fluid passages and thus delayed response time. The high pressure circuit may also comprise long fluid passages between the master and slave pistons, which disadvantageously increase the compressed fluid volume and thus the response time.
In addition, in conventional compression braking systems, the braking system is a bolt-on accessory that fits above the overhead. In such systems, in order to provide space for mounting the braking system, a spacer is positioned between the cylinder head and the valve cover. The valve cover is bolted to the spacer, which adds unnecessary height, weight, and costs to the engine. Many of the above-noted problems result from viewing the braking system as an accessory to the engine rather than as part of the engine itself.
One possible solution is to integrate components of the braking system with the rest of the engine components. One attempt at integrating parts of the compression braking system is found in U.S. Pat. No. 3,367,312 to Jonsson, which discloses an engine braking system including a rocker arm having a plunger, or slave piston, positioned in a cylinder integrally formed in one end of the rocker arm. The plunger may be locked in an outer position by hydraulic pressure in order to permit braking system operation. Jonsson also discloses a spring for biasing the plunger outward from the cylinder into continuous contact with the exhaust valve to permit the cam-actuated rocker lever to operate the exhaust valve in both the power and braking modes.
In addition, a control valve is used to control the flow of pressurized fluid to the rocker arm cylinder so as to permit selective switching between braking operation and normal power operation. The control valve unit is positioned separately from the rocker arm assembly, however, which results in unnecessarily long fluid delivery passages and therefore a longer response time. This may also lead to an unnecessarily large amount of oil that must be compressed before activation of the braking system can occur, resulting in less control over the timing of the compression braking.
Jonsson also discloses using the control valve to control the flow of fluid to a predetermined set of cylinders in the engine, thereby undesirably preventing individual engine cylinders or different groups of engine cylinders from being selectively operated in the braking mode.
Furthermore, the control valve as disclosed by Jonsson is a manually-operated, rotary type valve requiring actuation by the driver. Manual operation often results in unreliable and inefficient braking operation. Also, rotary valves are subject to undesirable fluid leakage between the rotary valve member and its associated cylindrical bore.
Other designs known in the art include U.S. Pat. No. 3,332,405 to Haviland, assigned to the assignee of the present application and incorporated herein by reference. Haviland discloses a compression braking system with a control valve unit for enabling the formation of a hydraulic link. The control valve unit is mounted in a cavity formed in a rocker arm that operates the exhaust valves during the braking mode. Separate cam lobes are used for normal power operation and braking operation. However, a single rocker arm is used to actuate the exhaust valves during both normal and braking modes. A drawback in this design is that the braking cam lobe profile design, and therefore the braking system operation, may be at least partially dependent on, or influenced by, the design of the cam lobe used for operating the exhaust valve during normal engine operation.
Another known design is disclosed in U.S. Pat. No. 4,251,051 to Quenneville, assigned to the assignee of the present application and incorporated herein by reference. Quenneville discloses a solenoid valve assembly with an inlet communicating with a supply of fluid, and one or more outlet passages communicating with respective loads requiring intermittent fluid supply and a drain passage. A respective ball valve is positioned between the inlet and each outlet and is spring-biased to block flow between the supply and outlet passage while opening the drain passage. An armature and pin are actuated to move the ball valve so as to connect the supply to the outlet and close the drain passage. However, while the valve assembly in the actuated position permits supply flow to the outlet passage, it does not prevent the return flow of fluid from the outlet passage into the supply passage and therefore does not permit the formation of a hydraulic link between different pressurized circuits as required by a control valve during compression braking system operation.
Designs in the known art have required independent check and shuttle valves in order to control a lost motion integrated rocker brake. Accordingly, there is a need for a simplified rocker brake control valve assembly. The design of the present invention integrates the check and shuttle valves into a single unit. This single unit serves to control the flow of oil within the integrated lost motion rocker brake. In addition, there have been many attempts to design systems to clip or reset lost motion circuits. The present invention also provides a system and method to allow the clipping or resetting of a lost motion engine brake system.
The present invention meets these needs and provides other benefits as well.
It is therefore an object of the present invention to provide an economical control valve for an integrated lost motion rocker brake.
It is another object of the present invention to provide a simplified means of controlling the flow of hydraulic fluid in an integrated lost motion rocker brake.
It is still another object of the present invention to provide an improved means of switching an engine brake between positive power and braking.
It is yet another object of the present invention to provide control of an integrated lost motion rocker brake without using an independent check valve and shuttle valve.
It is a further object of the present invention to provide an integrated lost motion rocker brake with a single valve having the same function as a known check valve and shuttle valve.
It is still a further object of the present invention to provide a control valve with a shuttle valve that indexes to direct the flow of hydraulic fluid in an integrated lost motion rocker brake.
It is yet a further object of the present invention to provide a control valve that permits a constant directional (checked) flow of hydraulic fluid for automatic lash adjustment in an integrated lost motion rocker brake.
It is another object of the present invention to provide an integrated lost motion rocker brake with a control valve that allows check hydraulic fluid to fill behind the accumulator, thereby preventing the accumulator from indexing.
It is still another object of the present invention to provide a control valve for clipping or resetting an engine valve in a lost motion system.
It is yet another object of the present invention to provide means of clipping or resetting an engine valve in a lost motion system and thereby to prevent the need for piston pockets.
It is another object of the present invention to provide an indexed or rotated valve located in the rocker arm or shaft of an integrated lost motion rocker brake.
Additional objects and advantages of the invention are set forth, in part, in the description which follows and, in part, will be apparent to one of ordinary skill in the art from the description and/or from the practice of the invention.
In response to the foregoing challenge, Applicant has developed an innovative and economical design for a single control valve for a lost motion integrated rocker brake. As illustrated in the accompanying drawings and disclosed in the accompanying claims, the invention is a braking system for an internal combustion engine having an engine valve selectively openable in response to movement of a rotary cam about a cam shaft and a rocker assembly cooperative therewith, and having a control valve hydraulically connected to an engine valve assembly and thereby to the engine valve, wherein the engine is operable in either a power mode or a braking mode, having an improvement comprising means for checking hydraulic fluid to provide constant directional flow of hydraulic fluid for automatic lash adjustment of a valve actuating piston having an upper end and a lower end; and means for controlling a supply of hydraulic fluid in order to provide actuation of the engine valve by the piston.
In an embodiment of the braking system of the present invention, the engine valve assembly may further comprise an accumulator slidably disposed in an accumulator bore in the upper end of the piston, the accumulator being biased upward by an accumulator spring, having a swivel foot disposed on a valve stem of the engine valve, and wherein the lower end of the piston is in contact with the swivel foot. The braking system of the present invention may combine the hydraulic fluid checking means and the controlling means together in the control valve.
The control valve may further comprise a control valve body having an upper end and a lower end and being slidably disposed in a control valve bore in the rocker arm and biased upward by a control valve spring, an inner body having a ball seat formed therein, and a check ball disposed in the inner body and biased upward by a check spring.
The control valve body may further comprise an upper annulus located toward the upper end of the control valve body, a lower annulus located toward the lower end of the control valve body, a middle annulus located around the control valve body between the upper annulus and the lower annulus, a first horizontal bore which diametrically spans the control valve body, having each end of the first horizontal bore opening within the upper annulus, and a second horizontal bore, which diametrically spans the control valve body, having each end of the second horizontal bore opening within the middle annulus, and wherein a first vertical bore and a second vertical bore are axially disposed in the inner body about a longitudinal axis.
In the braking system of the present invention, the check ball may be disposed in the second vertical bore, and the first vertical bore may connect the first horizontal bore with the second horizontal bore to provide hydraulic communication from the upper annulus, through the control valve body, to the middle annulus.
The braking system may further comprise a hydraulic system having a switched low pressure supply circuit and a constant low pressure supply circuit connected to the hydraulic fluid supply and to the control valve, and a lashless fluid supply circuit and an accumulator control circuit connecting the control valve to the engine valve assembly. Upon activation of a solenoid switch in braking mode, the control valve may index in the control valve bore, aligning the middle annulus with the lashless fluid supply circuit and the accumulator control circuit so that the lashless fluid supply circuit and the accumulator control circuit become hydraulically locked and the motion of the cam is translated directly into the motion of the engine valve.
In the braking system of the present invention, the hydraulic fluid controlling means may further comprise an accumulator control circuit and a switched low pressure supply circuit for providing clipping of the valve actuating piston and thereby provide lost motion braking. The braking system may further comprise a clipping/reset spool disposed in the cam shaft, and the clipping/reset spool may further comprise a plurality of clipping annuluses described therearound.
In the braking system of the present invention, the plurality of clipping annuluses may each form a reduced diameter about only a portion of the clipping/reset spool, such that when the reduced diameter portion is aligned with a clip passageway and thereby with the accumulator control circuit, hydraulic fluid dumps into the supply of hydraulic fluid, and when a full outer diameter portion of the clipping/reset spool is aligned with the clip passageway and thereby with the accumulator control circuit, the accumulator control circuit is closed and hydraulically locked, and the rocker assembly follows a braking bump on the cam.
In addition, Applicant has developed an innovative and economical design for clipping or resetting of a lost motion engine brake system. As embodied herein, the invention is a braking system for an internal combustion engine having an engine valve selectively openable in response to movement of a rotary cam about a cam shaft and a rocker assembly cooperative therewith, and having a control valve hydraulically connected to an engine valve assembly and thereby to the engine valve, wherein the engine is operable in either a power mode or a braking mode, and the improvement comprising a clipping/reset spool disposed in the cam shaft and connected to an accumulator control circuit, wherein movement of the clipping/reset spool provides clipping of a valve actuating piston and thereby lost motion braking, and wherein the clipping/reset spool further comprises a plurality of clipping annuluses described therearound, the plurality of clipping annuluses each forming a reduced diameter about only a portion of the clipping/reset spool, such that when the reduced diameter portion is aligned with a clip passageway and thereby with the accumulator control circuit, hydraulic fluid dumps into the supply of hydraulic fluid, and when a full outer diameter portion of the clipping/reset spool is aligned with the clip passageway and thereby with the accumulator control circuit, the accumulator control circuit is closed and hydraulically locked, and the rocker assembly follows a braking bump on the cam.
In the clipping/reset braking system, the accumulator control circuit may further comprise a check valve biased by a check valve spring, wherein the check valve checks a supply of hydraulic fluid in the accumulator control circuit.
It is to be understood that both the foregoing general description and the following detailed description are exemplary and explanatory only, and are not restrictive of the invention as claimed. The accompanying drawings, which are incorporated herein by reference, and which constitute a part of this specification, illustrate certain embodiments of the invention, and together with the detailed description serve to explain the principles of the present invention.